The present invention relates to a USB hub and a control method of USB hub, in particular to a USB hub and a control method of USB hub for connecting an upstream device and a downstream device by USB.
In recent years, USB (Universal Serial Bus) is widely used as an interface that connects between electronic devices. USB can connect a host device and various peripheral devices (devices). USB is used for plug-and-play and bus power which supplies electrical power through a USB cable. Further, the transfer speed of USB is improved. Therefore, USB is used in many devices. USB is used not only between electronic devices, but also inside an electronic device. For example, an USB interface is implemented in a semiconductor integrated circuit to connect between semiconductor chips and to connect between functional blocks inside a semiconductor chip.
A USB hub, which connects between a host device and a plurality of peripheral devices in order to enable USB connecting between a host device and many peripheral devices, is known. The USB hub has a plurality of USB ports to connect to a plurality of peripheral devices, so that even when the host device has only a small number of USB ports, the host device can connect to much more peripheral devices. The USB hub includes a USB controller for controlling the USB connectings.
For example, Non-Patent Documents 1 and 2 are known as USB controllers of related art. In particular, Non-Patent Document 1 describes a hub controller that controls a USB hub. “Ethernet” is a registered trademark.
[Non-Patent Document 1]
    SMSC, “USB 2.0 Hub and 10/100 Ethernet Controller (LAN9512/LAN951”, the Internet <URL:http://www.smsc.com/media/Downloads_Public/Data_Sheets/95 12.pdf>[Non-Patent Document 2]    Intel, “Intel 5 Series Chipset and Intel 3400 Series Chipset”, the Internet <URL:http://www.intel.com/Assets/PDF/datasheet/322169.pdf>